1. Field of the Invention
This invention relates to yarn handling apparatus and more specifically to apparatus suitable for transmitting by friction a false-twist to the yarn progressing therethrough, which procedure is useful in many texturing and other applications.
2. Description of the Prior Art
The technique of applying a false twist by friction to a moving yarn has been known for a long time. The technique comprises, broadly speaking, setting the moving yarn in contact with a moving surface, displacing it transversely with respect to the path of the yarn so that the yarn is twisted upstream of where the yarn is manipulated and permitting the yarn to regain its original twist downstream thereof.
This technique, for which many applications have been foreseen, has mainly been utilized for texturing synthetic yarns. That is, by applying false-twist to such yarns while also applying a thermal heating and cooling upstream of the false-twist element, such yarn is provided with volume and elasticity.
However, other applications of using false-twist have been proposed. For example the literature suggests false twisting in the context of producing fancy yarns, yarns having alternate twists along their lengths, autotwisted yarns, and the like.
Thus, it has been proposed in U.S. Pat. No. 3,415,048 to obtain alternate twist yarns, that is, to produce yarn having successive zones with "S" and "Z" twist along the yarn length, by utilizing a false-twist spindle and by changing the twist insertion length upstream of the spindle, according to a selected frequency.
Several embodiments for providing false twist have been proposed which provide a moving surface for communicating a twist by friction to a yarn. Those presently used in the texturizing field either employ bushings against which the yarns is urged into contact (internal friction false twisting) or overlapping discs mounted on parallel axles, the moving yarn contacting the outer surface of these discs (external friction false twisting).
It has also been proposed in French Pat. Nos. 1,191,361 and 1,255,922 and in U.S. Pat. No. 2,908,133 to utilize as a means for inserting the false twist, one or several endless belts or aprons against which the yarn rubs.
As illustrated in French Pat. No. 1,147,515 (U.S. Pat. No. 2,943,433) it has been proposed to thread the yarn between two moving aprons, these aprons being arranged diagonally with respect to each other in such a way that an impulsion is conferred in the direction of their displacement during the passage of the yarn between the aprons.
However, as set forth therein, the device must operate at relatively low speed in that it is necessary, where the aprons cross, to guide them exactly according to parallel planes and to keep the aprons at a distance from one another slightly smaller than the yarn thickness for which it is desired to provide the false twist. This implies a complex apron guidance system.
Further, the aforementioned patent presents an alternate embodiment wherein the aprons are replaced by two hyperboloids which are driven in rotation, the crossing angles between the axis thereof being at an angle of between 30 and 45 degrees, the yarn passing between them along a straight line crossing both of the hyperboloid axes at equal angles.
Although the embodiment described therein appears somewhat attractive, it has the disadvantage of utilizing parts having a complicated shape, making it difficult also to feed and otherwise adjust. And, as in the case of the apron device therein described, the device is rather cumbersome owing to the fact that the two parts in between which the yarn passes are arranged one on top of the other.
Furthermore, although the contact surface of the two hyperboloids is a straight line, it is practically impossible to maintain the yarn according to such straight line, which therefore leads to a variable action of the hyperboloids on the yarn.
Finally, with regard to the superimposed crossed apron device described in that patent, it has been noticed that in normal operation, they tend to displace themselves laterally on their guide roller, which displacement, of course, disturbs their intended functioning.
Therefore, it is an object of the present invention to provide an improved and perfected device permitting the communication of false-twist by friction to a moving yarn by means of endless aprons, which have the actual advantages of the formerly proposed apron device shown in U.S. Pat. No. 2,943,433, but without the disadvantages thereof particularly owing to the fact that the invention incorporates a scheme for reducing the volume of the apparatus of the prior art device and assures a mutual contact between both aprons in a much more precise manner than theretofore achieved.